The present invention relates to read channels in storage devices. In particular, the present invention relates to determining a signal-to-noise ratio for a read signal in a storage device.
In data storage devices, data that has been written to a storage medium is read from the medium through a read channel. Specifically, a read signal is generated by a read head that passes over the medium. The read signal is provided to the read channel where it is equalized to have a desired shape and is sampled by an analog-to-digital converter. The digital samples are then provided to a detector, such as a Viterbi detector, which determines a most likely sequence of values that could be represented by the digital samples.
One measure of the performance of a drive is the signal-to-noise ratio at the input to the Viterbi detector. Since this ratio involves an equalized read signal, it is referred to as an Equalized Signal-To-Noise Ratio (ESNR).
In the past, determining the ESNR for a drive required a Digital Storage Oscilloscope to over-sample the analog signal from the head and a software program to equalize the analog signal based on a model of the nominal equalization provided by the read channel. The resulting signal provided by the software program was then re-sampled to provide samples that could be used in the equalized signal-to-noise calculation. The use of such external devices was costly, time consuming and not completely accurate.
The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
A method and data storage device determine an equalized signal-to-noise ratio in the storage device. The equalized signal-to-noise ratio is determined by generating an analog read signal, passing the read signal through an equalizer in the storage device, and sampling the equalized signal using an analog-to-digital converter in the storage device. The samples from the analog-to-digital converter are then used in the equalized signal-to-noise calculation.